Check valves, operable to permit flow only in one direction, are well known and widely used in various applications. The conventional check valve, however, does not provide for a normal two-way flow in normal operation of the apparatus in which it is utilized. Hydraulic lifts are also well known and widely used in various applications, one of which is in tail gate lifts for transport trucks, for lifting heavy loads from ground level to the level of the truck bed, and vice versa, lowering such loads to the ground at a delivery point. If the hydraulic lift mechanism of such apparatus were to suddenly fail when the load platform is in an elevated position, the sudden collapse of the platform and its lift linkage could cause injury to workmen operating the lift and damage to merchandise (e.g. refrigerator, stove, etc.) being handled by the lift. Such a lift is disclosed in my U.S. Pat. No. 3,369,679.